Thermal processing systems are widely used in various stages of semiconductor fabrication. Basic thermal processing applications include chemical deposition, diffusion, oxidation, annealing, silicidation, nitridation, and solder re-flow processes. Vertical rapid thermal processing (RTP) systems have a vertically oriented processing chamber that is heated by a heat source such as a resistive heating element or a bank of high intensity light sources. An elevator tube is controlled to move a wafer on a wafer support vertically within the processing chamber. In some RTP systems, the heat sources create a temperature gradient within the processing chamber and temperature ramp-up and ramp-down rates of the wafer being processed are controlled by the vertical location of the wafer within the processing chamber. Therefore, to optimize the thermal processing of semiconductor wafers it is important to accurately control the position of the wafer within the processing chamber.
Prior art wafer supports, such as shown in FIG. 1, use pins, rings, or other hard surfaces to support the wafer during thermal processing. The prior art systems give rise to local contact type stresses and bending stresses. The silicon wafer yield strength decrease as a function of temperature. When the yield strength reaches the bending stress, microcracks may occur within the silicon crystal structure. This is detrimental at the point the wafer contacts the mechanical support. As processing temperatures increase, the potential for deformation becomes more significant.